- Email: [email protected]
Impact and other newer factors
Oral Oncology 45 (2009) 1005
Contents lists available at ScienceDirect
Oral Oncology journal homepage: www.elsevier.com/locate/oraloncology
Editorial
Impact and other newer factors
The impact factor (IF) has now been in use for some years, is well recognized by most readers, and may have some utility – but the disadvantages are also increasingly recognized.1 The five year Impact Factor, calculated in the same way as the regular IF, but measuring citations over a five year window rather than the two year window period of the regular IF, may reflect more accurately the impact of a journal. It has also been in use for some years. A new way of measuring journal influence is the EigenfactorTM . Like the IF, the EigenfactorTM score is essentially a ratio of number of citations to total number of articles. EigenfactorTM is however, an estimate of the percentage of time that library users spend with a particular journal – which differs from the IF in that each citation is weighted according to the (importance) of the source. It weights each reference according to a stochastic measure of the amount of time researchers spend reading the journal. It excludes self citations but it counts citations to journals in both the sciences and social science. Each citation is given a value greater or lesser than 1 based on the EigenfactorTM of the citing journal. A five year window of measurement is used (so the 2008 EigenfactorTM examines citations received in 2008 from articles published 2003–2007). Thomson Reuters now include EigenfactorTM metrics in Journal Citation Reports (JCR) but they are available only for years 2007 and later. EigenfactorTM scores are scaled so that the sum of the EigenfactorTM scores of all journals listed in JCR is 100. A journal EigenfactorTM score is a measure of the journal’s total importance to the scientific
1368-8375/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.oraloncology.2009.10.001
community. With all else equal, a journal’s EigenfactorTM score doubles when it doubles in size and thus a large journal will have high EigenfactorTM scores simply based upon the journal size. Disadvantages however, include that the current EigenfactorTM method means that a good paper published in a low profile journal will not be weighted as highly as a mediocre paper in a more high profile journal.2 Interestingly, and perhaps most importantly for readers, the two metrics EigenfactorTM and IF have been shown to be strongly correlated for medical journals.3,4 References 1. Scully C, Lodge H. Impact factors and their significance; overrated or misused? Brit Dental J 2005;198:391–3. 2. http://www.eigenfactor.org/faq.htm. 3. Davis PM. Eigenfactor: does the principle of repeated improvement result in better estimates than raw citation counts? J Am Soc Inform Sci Technol 2008;59:2186–8. 4. Fersht A. The most influential journals: impact factor and eigenfactor. Proc Natl Acad Sci USA 2009;106(17):6883.
Crispian Scully UCL–EDI 256 Gray’s Inn Road, London WC1X 8LD, UK E-mail address: [email protected] Available online 5 November 2009
Contents lists available at ScienceDirect
Oral Oncology journal homepage: www.elsevier.com/locate/oraloncology
Editorial
Impact and other newer factors
The impact factor (IF) has now been in use for some years, is well recognized by most readers, and may have some utility – but the disadvantages are also increasingly recognized.1 The five year Impact Factor, calculated in the same way as the regular IF, but measuring citations over a five year window rather than the two year window period of the regular IF, may reflect more accurately the impact of a journal. It has also been in use for some years. A new way of measuring journal influence is the EigenfactorTM . Like the IF, the EigenfactorTM score is essentially a ratio of number of citations to total number of articles. EigenfactorTM is however, an estimate of the percentage of time that library users spend with a particular journal – which differs from the IF in that each citation is weighted according to the (importance) of the source. It weights each reference according to a stochastic measure of the amount of time researchers spend reading the journal. It excludes self citations but it counts citations to journals in both the sciences and social science. Each citation is given a value greater or lesser than 1 based on the EigenfactorTM of the citing journal. A five year window of measurement is used (so the 2008 EigenfactorTM examines citations received in 2008 from articles published 2003–2007). Thomson Reuters now include EigenfactorTM metrics in Journal Citation Reports (JCR) but they are available only for years 2007 and later. EigenfactorTM scores are scaled so that the sum of the EigenfactorTM scores of all journals listed in JCR is 100. A journal EigenfactorTM score is a measure of the journal’s total importance to the scientific
1368-8375/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.oraloncology.2009.10.001
community. With all else equal, a journal’s EigenfactorTM score doubles when it doubles in size and thus a large journal will have high EigenfactorTM scores simply based upon the journal size. Disadvantages however, include that the current EigenfactorTM method means that a good paper published in a low profile journal will not be weighted as highly as a mediocre paper in a more high profile journal.2 Interestingly, and perhaps most importantly for readers, the two metrics EigenfactorTM and IF have been shown to be strongly correlated for medical journals.3,4 References 1. Scully C, Lodge H. Impact factors and their significance; overrated or misused? Brit Dental J 2005;198:391–3. 2. http://www.eigenfactor.org/faq.htm. 3. Davis PM. Eigenfactor: does the principle of repeated improvement result in better estimates than raw citation counts? J Am Soc Inform Sci Technol 2008;59:2186–8. 4. Fersht A. The most influential journals: impact factor and eigenfactor. Proc Natl Acad Sci USA 2009;106(17):6883.
Crispian Scully UCL–EDI 256 Gray’s Inn Road, London WC1X 8LD, UK E-mail address: [email protected] Available online 5 November 2009